1. Field of the Invention
The present invention relates to an electronic device, which is represented by a crystal oscillator piece or a piezoelectric element, and to a method of manufacturing an electronic device.
2. The Related Art
A crystal oscillator has excellent frequency characteristics and is thus widely used as one device, specifically, as a printed board mounting component. The crystal oscillator is preferably accommodated in a sealed casing to block the effect of outside air, such that the characteristics of the crystal oscillator are stabilized. An example of such a package structure is described in “glass-ceramic composite and flat package type piezoelectric component using the same” (JP-A-11-302034) or the like.
JP-A-11-302034 describes an electronic device which has a crystal piece placed on a base with a cap. In this case, a package is formed by using a mixture of ceramic and glass powder having substantially the same thermal expansion coefficient as the crystal piece.
However, according to the technique described in JP-A-11-302034, since the package is formed of a glass-ceramic composite, the crystal piece is placed on a single base and the cap is put over the crystal piece, that is, single-part production is provided. For this reason, productivity is considerably low. Further, it is difficult to process the glass-ceramic composite, and production cost increases.
In order to resolve these problems, a method has been suggested in which a package is manufactured by easy-to-process glass. This method is described in “electronic component package” (JP-A-2003-209198) or the like.
The summary of JP-A-2003-209198 will be described with reference to FIG. 6. According to the technique described in JP-A-2003-209198, a method of manufacturing an electronic device 100 includes the steps of FIG. 6A forming a through hole in a base 110, FIG. 6B flowing low-melting-point glass into the through hole and inserting a metal pin 120, FIG. 6C fitting a metal pin 120 and recessing the glass board, FIG. 6D forming an electrode 130 by printing, FIG. 6E mounting a component, such as a crystal oscillator, on the metal pin, and FIG. 6F sealing and bonding a cap 160 and the base 110 through a sealant 150. Of these, in the step FIG. 6C, the heating temperature is equal to or higher than the softening point of glass (about 1000° C.) and glass is welded, such that the metal pin 120 is fixed closely to the base 110. Therefore, airtightness can be reliably ensured in the step FIG. 6F and the electronic device can be manufactured at low cost.
According to the manufacturing method of the electronic device 100, in the step FIG. 6C, there is a problem shown in FIG. 7. FIG. 7 is an enlarged view of the metal pin portion in the step FIG. 6C. That is, as shown in of FIG. 7A, when the metal pin 120 is short or when the fitting amount is small, low-melting-point glass 170 includes the metal pin 120. For this reason, it is impossible to ensure electrical connection between the electrode 130 which is formed in the step FIG. 6D and the metal pin 120. Further, as shown in FIG. 7B, even when the metal pin 120 is fitted as designed, since the base 110 is at a temperature equal to or higher than the softening point, glass may cover the front end of the metal pin 120. In addition, as shown in FIG. 7C, the metal pin 120 is at a temperature of about 1000° C., an oxide film 180 is grown in the vicinity of the metal pin 120, and electrical conduction is not provided between the electrode 130 and the electronic component 140.